In cleaning systems removing contaminants from electronic components, a technique utilizing supercritical carbon dioxide is used. A cleaning system of this type includes a washing chamber for treating a cleaning object, a separating chamber for separating removed contaminants and carbon dioxide, and a pumping member for pumping supercritical carbon dioxide fluid. The cleaning object is placed in the washing chamber, carbon dioxide fluid pressurized to a predetermined pressure is fed thereto, and contaminants adhering to the cleaning object are extracted into the carbon dioxide fluid. The resulting carbon dioxide fluid containing the contaminants is introduced into the separator, and the separating chamber is then decompressed to a predetermined pressure to separate the contaminants and the carbon dioxide fluid. The carbon dioxide fluid is recycled, and the cleaning object is retrieved from the washing chamber after the pressure of the washing chamber is decreased, thereby finishing this cleaning treatment.
As described above, such a technique in which supercritical carbon dioxide is used for cleaning electronic components has been conventionally known. The inventors have conducted intensive research on using supercritical fluid such as supercritical carbon dioxide in other applications. As a result, the inventors developed an apparatus and method for forming a thin-film using supercritical fluid.
A sol-gel solution and so on, which are used for forming a metal oxide thin-film by a spin coating process or the like, contain an alcohol solvent such as n-butylalcohol having a relatively large molecular weight and low volatility such that the solution can be preserved for a long term. This is because a change in composition and a change in thickness caused by the vaporization of the alcohol solvent are prevented as much as possible. On the other hand, there is a problem that carbon, which is a main component of the alcohol solvent, remains in an obtained metal oxide thin-film because the alcohol solvent has a relatively large molecular weight and low volatility.
The present invention has been made in order to solve the above problems. It is an object of the present invention to provide an apparatus and method for forming a thin-film using raw material fluid containing supercritical fluid or liquid and raw materials for such a thin-film.